Communication cable comprising one or more screened core groups



Feb. 22, 1938. H. KADE'N ET AL COMIUNICATION CABLE COMPRISING ONE ORMORE SCREENED CORE GI QOUPS Filed July 17, 1935 73 7 'olvoacme Javaaxe-am ft-rnluc swarm HM m, H; WW v Patented Feb. 22 1938 PATENT OFFICECOMMUNICATION CABLE COMPRISING ONE OR MORE SCREENED CORE GROUPS HeinrichKaden, Berlinsiemensstadt, Paul Thomas, Berlin-Wilmersdorf, and HansWassmansdoril, Berlin- Spandau, German Y, on; to Siemens 8: Halske,Aktiengesellschaft, Siemenssiadt, near Berlin, Germany, a corporation ofGermany Applicaiion'luly 17, 1935, Serial No. 31,780

In Germany July 17, 1934 8 Claims. (01. 173 81) Our invention relates toimprovements in communication cables comprising one or more screenedcore groups.

- As is known, the arrangement of conductive screens in communicationcables is an eflective means of reducing the crosstalk interferencesbetween the dlfierent lines and the interferences arising from externalsources of disturbance. To obtain as large a screening effect aspossible, the screening sleeves must be as highly conductive as possibleand, if possible, form a closed tube, that ,is, a tube having acontinuous unbroken wall. Since, however, a closed tube is, on the onehand, comparatively expensive to produce and, on the other hand, is notvery flexible, the screens in communication cables are usually made inthe form of tape'windings, the tapes consisting for example of tinfoil,metallized paper or of magnetizable material. Such screens in general,are sufllclent for low-frequency transmission. In order to obtain withmore stringent requirements as to freedom from crosstalk, for examplewith higher frequency of the communication currents and with high lineattenuation, a sufliciently great screening efiect, it has been proposedto arrange a number of screens consisting of tape windings, one on theother. Such multiple screens are, however, comparatively expensive andmaterially increase the diameter of the cable.

The present invention provides'a novel construction of the screens andis based on the fact hitherto unknown that the paths oi ;the eddycurrents produced by the communication currents,

extend in the direction of the cores? According to the invention, thereare arranged around the core group to be screened, for example, a pairor quad, a number of good conducting tapes or wires, generically termedin some of the annexed claims as strand elements, which are laid andtwisted in the same direction as that in which the cores of the coregroup a stranded.

Preferably also, t "e stranding lay or length of the pitch of thescreening strand elements is made to agree with the length of twist orpitch of the core group.

In this way, the eddy currents induced in the screen, which follow thetwist of the core group, are caused to flow in a metallic layer of smallresistance. In previous constructions of the the eddy currents meet'with a large resistance at the abutting edges of the adjacent turns ofthe tape winding. Consequently, with the screens made in the prior artform of short pitch tape 55 windings, the eddy currents cannot developto an screens in the form of short pitch tape windings,

extent which is necessary for the screening of the magnetic field of thelead jacket 01. the cable. The consequence is that the magnetic field,as a result of the insufllcient screening eflect, penetratesinto thelead jacket and with high frequencies causes heavy losses therein, sincethe additional losses caused by the lead jacket in the case of highfrequencies increase with the square root of the specific resistance ofthe material of the sleeve. invention, a screenis arranged over the coregroup consisting of longitudinally twisted strand elements having thesame direction 01' stranding as that of the core group, then theresistance of the screen to the eddy currents is small and consequentlythe screening eilect is large.

The screen is, as far as possible, made as a closed stranded layer. Asimple form 01 construction consists of a number of thin tapes strandedso as mutually to overlap one another at the side edges. Furthermore,two layers of tapes may be stranded one over the other in such mannerthat the tapes of the outer layer If, however, in accordance with thecover the gaps between or the abutting edges of the tapes of the innerlayer. Further embodiments of the invention consist in making the screenby an alternating arrangement of single and double tape strands in whichthe lateral edges of the single strands are located between the lateraledges of the double strands, or else all strands may consist of doubletape and one lateral edge of each strand may be'located between the nextadjacent lateral edges of one of the adjoining strands. Thus in eachcase a closed screening layer is formed.

The screens made in accordance with the invention are suitable for usewith particular advantage for high frequency cables, for example, formultiple carrier frequency cables, and for television cables whichcontain only a single core group, in order to avoid the eddy currentsotherwise arising in the lead jacket when high frequency currents areused.

If the screen tapes or wires are stranded with the same length of lay ortwist pitch and the same direction of twist as the cores of the coregroup to be screened, the danger exists of these ing material or asupplementary supporting memher, for example, an open wire winding isarranged underneath the screen.

In. the screen consisting of longitudinally twisted tapes there is alsothe danger that when the cable is mechanically stressed, especially inbending, the tapes become displaced over each other so that gaps occurwhich more or less impair the action of the screening sleeve. Forexample,

electric or magnetic internal or external fields can penetrate throughthe gaps of the metal screens and. thus produce interferences and thisparticularly affects cables for the transmission of very highfrequencies. Hitherto, there has been no possibility of securing tapesarranged with long lay or pitch in their positions with respect to eachother, so that it has been necessary either to use shorter lengths oflay or pitch for the tapes which is undesirable for electrical reasonsand also on account of the increase in the cost of making the cable, orit has been necessary to give the tapes a particular shape in order tosecure their position, which, however, is still more expensive than theuse of shorter lengths oflay.

It would be, for example, possible to use profiled lengths of Z-shape incross section which while engaging securely in each other, are thick anduse of a number of layers of thin metallized paper.

tapes and the like, has again the disadvantage that the tapes have toogreat an electric resistance, so that they do not sufiice for screeningstrong fields, especially magnetic fields and, furthermore, cannotprovide any mechanical protection to the cores.

In order to secure metal tapes laid with a long twist in their relativepositions, in accordance with the invention, there are inserted in avery advantageous manner, between the thin and wide screening tapes andalternating with them, thicker and narrower shaped lengths of material,such as round wires. with the same twist lay.

These thicker, narrower shaped lengths of material sufiice in asurprising manner entirelyto prevent the thin wide tapes from shiftingover each other so that the core groups or thewhole cable core protectedby screens formed by the tapes can be bent round a curve of any desiredsmall radius, without the tapes shifting over each other or gaps beingotherwise produced between them. If the alternating tapes and/or wiresare to be secured in position even more firmly, this can be effected bythe application of an additional wire or tape with a different lay-around the screen, preferably with a lay of like direction but shorterpitch than the screen tapes and in widely spaced helical windings. Theseadditional wires or tapes may consist of the same material as the screenor of a difierent material and may also be arranged to serve as requiredas a transverse conductive combining means for the protective tapes. I

A number of embodiments of the invention are shown in Figures 1 to 11 ofthe accompanying drawing, of which Figures 1 and 2 show one -form ofcable respectively in cross section and Figures 5 and 6 showrespectively cross sections of two further forms of cable; and

Figures 7 to 11 show respectively in diagrammatic form and-incross-section different constructions of screening sleeves built up inaccordance with the invention.

Figures 1 and 2 show a high frequency cable which comprisesa twisteddouble line the two conductors of which are indicated at I0 and l I. Theconductors are formed as thin hollow conductors which are each supportedupon an internal core l2 of insulating material. To form an air spaceinsulation, each conductor is surrounded with a helically wound cord l3and a sleeve M of insulating material is then applied in the form of atape winding. The two cores so built up are twisted together in commonwith filler elements l5 of insulating material.

Over the double line is first arranged a sleeve I6 of insulatingmaterial and over this is arranged a screen I! formed in accordance withthe invention. The screen I! consists of a closed layer formed ofthincopper tapes laid with a long length of twist and with overlapping oftheir edges. Over the conductive screen so formed a sleeve of insulatingmaterial I8 is applied in the form of a tape winding and then a leadjacket H9.

The high-frequency cable shown in Figures 3 and 4, differs from theembodiment shown in Figures 1 and 2 essentially only in that no suchadditional fillers as the fillers [5 in Figures 1 and 2 are provided forsupporting the conductive screen but instead a metal wire wound roundthe conductor pair in open helical turns is arranged under theconductive screen. In Figures 3 and 4, 2D and 2| indicate the twotubular conductors which are each supported on a core 22 consisting ofinsulating material. A cord 23 of insulating material is wound in openhelical windings around each conductor and is surrounded with a closedsleeve 24 of insulating material in the form of a tape winding. The twocores twisted together are then surrounded by a wire '25 wound in spacedhelical turns and then provided with a screen 26 built up of tapes ofgood conducting material in the same way as the screen I! in Figures 1and 2. Over the screen 26 a. sleeve 21 of insulating material isarranged in the form of a. tape winding, and then a lead jacket 28.

Figure 5 shows a communication cable comprising four' conductor pairs30, 3|, 32, and 33 in which the individual pairs are each surrounded bya screen formed in accordance with the invention. Each conductor pairconsists of the two tubular conductors 34 and 35 which are eachsurrounded by a cord 36 of insulating material and then by a sleeve 31also of insulating material. The two cores so formed are twistedtogether in combination with filler elements 38 of insulating materialand are surrounded with a conductive screen 39 and a sleeve 40 ofinsulating material. The conductive screen is built up of a number ofgood conducting tapes twisted with a long lay or pitch and overlappingone another at their edges. Over the four twisted pairs a sleeve ll ofinsulating material is applied and then a lead jacket.

The communication cable shown in Figure 6 differs from that shown inFigure 5 essentially only in that the cable is built up of spiral quadsinstead of pairs and the individual conductors are solid instead oftubular. The cable comprises four spiral quads 50, 5|, 52, and 53. Theindividual conductors in each quad are surrounded with a helically woundcord 54 and then surrounded with a sleeve 55 of insulating material.

Over each spiral quad a screen 56 is provided plied around the screen. Alead jacket 58 is provided for the cable.

Referring now to the forms of screens shown in Figures 7, 8, and 9, thatshown in Figure 7 consists of two layers of stranded tapes of which thetapes 60 of the outer layer cover the joints between the tapes 6| of theinner layer. The screen shown in Figure 8 consists of an alternatingarrangement of single metal tapes 62 and /64-. The screen shown inFigure 9 is built up en-.

tirely of superposed double tapes, the edges of which areslightly-spread apart on one side to form a fork-like arrangement intowhich the lateral edges of the adjacent pair of tapes extend, so that adouble closed metal screening sleeve is formed.

Figures 10 and 11 show two forms of screening sleeves in which betweenthe adjacent wide screening tapes thicker, narrower lengths of materialare inserted to prevent the tapes from becoming displaced one over theother. In the arrangement shown in Figure 10, comparatively thin butwide tapes 10 are laid on the cable core to form a screen, the corebeing of any desired form. Between adjacent tapes I0 and alternatingtherewith thicker, narrower lengths of material are inserted, theselengths consisting of round wires of greater thickness than the tapes.

The different thicknesses as of the wires and tapes lay or pitch thanthat of the tapes Hi and the wires ll. Practical experience has shownthat great security against displacement of the thin tapes 10 over oneanother is afforded by this arrangement and the amount of material usedfor the screen, in comparison to the amount contained in profiled wires,is very small. The tapes Ill may be relatively wider than those shown inthe drawing.

We claim as our invention:

1. In a long distance communication cable for low and high frequencies,having at least one group of cores twisted together about a common axis,a screen surrounding said group, said screen consisting of a pluralityof good conducting strand elementslaid side by side helically aroundsaid group and following individually the direction of the cores in saidgroup.

2. In a long distance communication cable for low and high frequencies,having at least one group of cores twisted together about a common axis,a screen surrounding said group, said screen consisting of -a pluralityof good conducting strand elements laid side by side helically aroundsaid group, and having the same twist direction and the same pitch asthe core twist.

3. In a long distance communication cable for low and high frequencies,having at least one group of cores twisted together about a common axis,a screen surrounding said group, said screen consisting of a pluralityof good conducting tapes, laid edge to edge helically around said groupand having the same twist direction and the same pitch as the coretwist, said tapes being laid in two superposed layers, the tapes in onelayer bridging the joints between the tapes in the other layer.

4. In a long distance commu \ication cable for low and high frequencies,having at least one group of cores twisted together about a common axis,a screen surrounding said group, said screen consisting of a pluralityof good conducting tapes, laid edge to edge helically around said groupand having the. same twist direction and the same pitch as the coretwist, at least every other tape of said screen consisting of doubletape layers, the adjacent edge of an'adjacent tape engaging between thetwo layers of the double tape.

5. In along distance communication cable for low and high frequencies,having at least one group of cores twisted together about a common axis,a screen surrounding said group, said screen consisting of a pluralityof good conducting tapes, laid edge to edge helically around said groupand having the same twist direction and the same pitch as the coretwist, each tape consisting of two superposed layers, one edge of eachtape having both of its layers interposed between the two layers of theadjacent tape edge.

6 In a long distance communication cable for low and high frequencies,having at least one group of cores twisted together about a common axis,a screen surrounding said group, said screen consisting of a pluralityof good conducting strand elements laid side by side helically aroundsaid group, and having the same twist direction and the same pitch asthe core twist, said strand;

consisting of a plurality of good conducting strand elements. laid sideby side helically around said group, and having the same twist directionand the same pitch as the core twist, and supporting means disposed onsaid twisted cores underneath said screen, for supporting the strandportions circumferentially suspended between the cores.

8. In a long distance communication cable for low and high frequencies,having at least one group of cores twisted together about a common axis,a screen surrounding said group, said screen consisting of a pluralityof good conducting strand elements laid side by side helically aroundsaid group, and having the same twist direction and the same pitch asthe core twist; and a supporting helical open wire winding of muchsmaller pitch than thatof the core twist, wound around saidv twistedcores for supporting the screen strand portions circumferentiallysuspended between the cores.

HEINRICH KADEN. PAUL THOMAS. HANS WASSMANSDORFF.

